1,014 research outputs found
Cosmic rays: extragalactic and Galactic
From the analysis of the flux of high energy particles, ,
it is shown that the distribution of the power density of extragalactic rays
over energy is of the power law, , with the same
index of that has the distribution of Galactic cosmic rays before so
called 'knee', . However, the average power of
extragalactic sources, which is of , at
least two orders exceeds the power emitted by the Galaxy in cosmic rays,
assuming that the density of galaxies is estimated as .
Considering that such power can be provided by relativistic jets from active
galactic nuclei with the power , we estimate the density of extragalactic sources of cosmic rays as
. Assuming the same nature of Galactic
and extragalactic rays, we conclude that the Galactic rays were produced by a
relativistic jet emitted from the Galactic center during the period of its
activity in the past. The remnants of a bipolar jet are now observed in the
form of bubbles of relativistic gas above and below the Galactic plane. The
break, observed in the spectrum of Galactic rays ('knee'), is explained by fast
escape of energetic particle, , from the Galaxy because of
the dependence of the coefficient of diffusion of cosmic rays on energy,
. The obtained index of the density distribution of particles
over energy, , for
agrees well with the observed one, . Estimated time of
termination of the jet in the Galaxy is years ago.Comment: 22 pages, 4 figure
Understanding diversity of human innate immunity receptors: analysis of surface features of leucine-rich repeat domains in NLRs and TLRs.
BackgroundThe human innate immune system uses a system of extracellular Toll-like receptors (TLRs) and intracellular Nod-like receptors (NLRs) to match the appropriate level of immune response to the level of threat from the current environment. Almost all NLRs and TLRs have a domain consisting of multiple leucine-rich repeats (LRRs), which is believed to be involved in ligand binding. LRRs, found also in thousands of other proteins, form a well-defined "horseshoe"-shaped structural scaffold that can be used for a variety of functions, from binding specific ligands to performing a general structural role. The specific functional roles of LRR domains in NLRs and TLRs are thus defined by their detailed surface features. While experimental crystal structures of four human TLRs have been solved, no structure data are available for NLRs.ResultsWe report a quantitative, comparative analysis of the surface features of LRR domains in human NLRs and TLRs, using predicted three-dimensional structures for NLRs. Specifically, we calculated amino acid hydrophobicity, charge, and glycosylation distributions within LRR domain surfaces and assessed their similarity by clustering. Despite differences in structural and genomic organization, comparison of LRR surface features in NLRs and TLRs allowed us to hypothesize about their possible functional similarities. We find agreement between predicted surface similarities and similar functional roles in NLRs and TLRs with known agonists, and suggest possible binding partners for uncharacterized NLRs.ConclusionDespite its low resolution, our approach permits comparison of molecular surface features in the absence of crystal structure data. Our results illustrate diversity of surface features of innate immunity receptors and provide hints for function of NLRs whose specific role in innate immunity is yet unknown
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